java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法 'java.lang.String android.os.Bundle.getString

Question

import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.util.Log;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SharedPreferences  
sharedPreferences=this.getSharedPreferences("com.example.sharedpre",Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString("username", "VJ").apply();
String user=savedInstanceState.getString("username","");
Log.i("username",user);
}
}

Answer 1

您需要换行，这会导致如下错误：

String user;
if (savedInstanceState != null) {
user = savedInstanceState.getString("username", "");
} else {
user = "";
}

Answer 2

在共享首选项中保存之前，请检查您的editText是否不是，然后检查您的savedInstanceState

if (savedInstanceState != null)